1. Field of the Invention
This invention relates to a method to limit strain relaxation of hetero-epitaxial III-nitride layers grown on III-nitride substrate/epilayers, by patterning said substrate/epilayer.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
In spite of numerous advantages offered by growth of optoelectronic devices on nonpolar/semipolar III-nitride substrates, misfit dislocation (MD) formation at misfitting heterointerfaces [1, 2] can make it difficult for device manufacturers to fully realize the expected inherent advantages. For semipolar III-nitride based devices, stress relaxation via glide of pre-existing threading dislocations can limit the composition/thickness of strained heteroepitaxial films that can be grown coherently on underlying substrates/films. This can, in turn, limit the device design space e.g. the range of emission wavelength for Light Emitting Diodes (LEDs)/Laser Diodes (LDs).
Additionally, performance for LDs can be affected due to poor optical waveguiding provided by thinner/lower composition waveguiding (typically InGaN) and cladding layers (typically AlGaN). The present invention provides a way to limit the stress-relaxation by the above mentioned glide process, and thus reduces the constraints on device design space, allowing employment of thicker/higher composition strained III-nitride alloy epitaxial layers. The proposed devices can be used as an optical source for various commercial, industrial, or scientific applications. These nonpolar or semipolar nitride LEDs and diode lasers can be expected to find utility in the same applications as c-plane nitride LEDs and diode lasers. These applications include solid-state projection displays, high resolution printers, high density optical data storage systems, next generation DVD players, high efficiency solid-state lighting, optical sensing applications, and medical applications.